This invention relates generally to ring lasers and particularly to ring laser gyroscope rotation sensors. Still more particularly, this invention relates to apparatus and methods for preventing plasma in the lasing medium of a ring laser gyroscope from impinging on mirrors used to direct the laser beam in a closed path.
Ring laser gyroscopes have been used in navigation systems for several years. A plurality of mirrors directs counterpropagating laser beams through a closed optical path defined by a plurality of passages or bores in a frame that is typically formed of a thermally stable glass/ceramic material. The laser beam is formed by applying a suitable voltage to a gain medium such as a mixture of Helium and Neon to produce a plasma. Electrons in the plasma emit light as they transition from a high energy state to a lower energy state. The optical path is formed to have a selected length so that a selected frequency of light produced in the gain medium resonates and is amplified.
To obtain the maximum optical signal it is necessary that the mirrors be as free of surface contaminants that degrade the reflectivity of the mirrors. Mirror contamination is a major factor in reducing the length of time for which a ring laser is considered to be useful in navigation system applications. As the ring laser operates, a small amount of the frame material becomes devitrified and mixes with the plasma. Some of the devitrified frame material is deposited on the mirror surfaces that are exposed to the plasma. This devitrified frame material slowly degrades the mirrors and reduces the laser intensity in the cavity.
The prior art solution to the problem of reducing ring laser mirror contamination is the use of various shielding techniques. Mirror shielding can be effective, but presently known mirror shields are costly to fabricate and install.